Study Associates Flame Retardants with Papillary Thyroid Cancer

Flame retardant chemicals (FRs) may be strongly linked to instances of papillary thyroid cancer (PTC), according to a new study.

In a press conference at the 99th Annual Meeting of the Endocrine Society in Orlando, Florida, Julie Ann Sosa, MD, of Duke University, stated the importance of such research

Sosa called her team’s work “Unique, in that it represents a transdisciplinary team approach,” that included endocrinologists, epidemiologists, and environmental chemists.

PTC is one of the fastest-growing forms of cancer in the United States, up 300% in the past 30 years. Thyroid cancer has crept up from the #8 cancer among women to #5 in the last decade, and by 2019 it’s expected to move up to #3, overtaking uterine and colorectal cancer. Sosa pointed to a recent JAMA article released only yesterday that indicated that PTC incidence is indeed rising, rather than just being diagnosed more.

“Coincident in this increase in thyroid cancer and papillary thyroid cancer, in particular, we have seen an increase in the amount of flame retardant chemicals in the environment. This is in part because of voluntary and mandatory flammability standards that have been established in this country,” she noted, pointing to FRs in furniture, upholstery, and electronics. Previous animal studies have indicated that flame retardants can disrupt thyroid function, and the chemical structure of FRs is markedly similar to thyroid hormone structure, but data involving FRs and their human impact is still somewhat scarce, according to Sosa.

For the study, the team recruited 70 patients with the disease and an equal number of age- and gender-matched controls, with an average age of 48 years old and nearly 80% of the cohort being female. In blood samples from the patients, the researchers tested for biomarkers associated with polybrominated diphenyl ethers (PBDE) FRs, and also collected dust samples from the participants’ homes. The levels of several of the FRs, including decabromodiphenyl ether (BDE-209) and tris(2-chloroethyl) phosphonate (TCEP), were found to be higher in the dust samples from the homes of the PTC patients than the controls. BDE was phased out of products in 2013.

Those with above-average levels of BDE-209 dust in the home were 2.29 times more likely to have TPC than those with lower levels (95% CI; 1.03, 5.08)

There were also different patterns of cancer aggressiveness associated with different retardants. There were higher levels of BDE associated with smaller and less aggressive tumors. Over the last ten years, Sosa says, these are the variety of tumors that have been increasing in incidence the fastest. Higher levels of TCEP were associated with larger, more aggressive tumors that extended outside of the thyroid: those with elevated levels of TCEP in the home were 4.14 times more likely to have PTC with that variety of tumors than those with below-median levels of it (95% CI; 1.01, 16.98)

With the incidence already high and continuing to rise, Sosa was adamant about the importance of exploring environmental factors. Other potential explanations may include the decline in tobacco use and rise in obesity (there is one cancer that tobacco is protective against).

In a line of questioning about prevention, she stressed that for too long the problem had been ascribed to over-diagnosing. Using the word “pandemic,” she discussed the need for environmental factors to be considered more.

“I think it behooves all of us to make a case to patients, the public, and policymakers particularly about the importance of resourcing science, innovation, and discovery in this specific arena,” she said.

“I think in the arena of flame retardants there’s long been an awareness of the value that they bring…but that has potentially come with a cost. I think what the challenge is for many of my colleagues in environmental science, if we understand what the cons are of many of these chemicals, then we can start to work on developing alternatives.”